The application of a physical adapter including a gas diffusion limiting aperture in combination with a solid electrolyte electrochemical cell is described in the above-identified cross-referenced related application which is incorporated herein by reference.
While the gas analyzer concept disclosed in the above-identified application provides an improved gas sensor apparatus for use in measuring gas constituents such as oxygen, sodium, etc., the concept as disclosed does not teach the gas diffusion aperture adapter in combination with the solid electrolyte electrochemical cell for monitoring combustibles or fuel constituents, of a combustibles gas environment. The term combustibles gas environment as used herein defines a gas environment wherein the combustibles or fuel constituents are in excess of the free oxygen.
In the non-combustibles sensing application described in the above-identified related application, the solid electrolyte electrochemical cell functions to pump the gas constituent of interest, i.e., oxygen, from an internal chamber formed by the combination of the solid electrolyte electrochemical cell and the gas aperture adapter. The diffusion rate of oxygen is proportional to the resulting current of the solid electrolyte electrochemical cell. Inasmuch as the rate of diffusion of the gas constituent of interest through the aperture is proportional to the content of the gas constituent in the gas environment, the solid electrolyte electrochemical cell current is a measurement of the presence of the non-combustible gas constituent of interest in the gas environment. In the invention of the above-identified application as well as that of the present application, the gas diffusion limiting aperture is the prime element in measuring a gas constituent and the solid electrolyte electrochemical cell functions in a secondary manner, i.e., not as a gas measuring element but rather as a gas pumping element.
In contrast to the above-identified related application wherein solid electrolyte electrochemical cell functions to pump the gas constituent of interest from the internal chamber formed by the gas aperture adapter and the solid electrolyte electrochemical cell, in the present invention a gas different from the gas constituent of interest is introduced into the internal chamber to combust with combustibles constituent diffusing through the aperture. This produces a differential pressure of the combustibles constituent across the aperture and establishes a diffusion of the combustible constituent from the combustible gas environment through the aperture into the internal chamber. The pumping potential is established at a level such that sufficient oxygen is introduced into the internal chamber to react with and deplete the combustibles constituent present in the internal chamber. The solid electrolyte electrochemical cell current resulting from the pumping of oxygen into the internal chamber is a function of the diffusion rate of the combustibles constituent through the aperture. This in turn is proportional to the combustibles content of the combustibles gas environment being monitored. The current of the solid electrolyte electrochemical cell is monitored as a measurement of the combustibles content of the combustibles gas environment.
An EMF measuring circuit indicates changes in the atmosphere of the internal chamber between a reducing atmosphere and an oxidizing atmosphere. This indication provides a basis for establishing the pumping potential at a level sufficient to assure introduction of sufficient oxygen to deplete the combustibles present in the internal chamber.